Without limiting the scope of the invention, its background is described in connection with heterojunction bipolar transistors (HBTs), as an example.
The design of power HBTs requires electrical and thermal considerations. The thermal design of a power HBT is very critical to reliable operation of the device. HBT's have similar characteristics to Si bipolar in that the base-emitter junction voltage, V.sub.BE, has a negative temperature coefficient.
The negative temperature coefficient of V.sub.BE gives rise to the possibility of "thermal runaway" condition (also known as "current hogging" or "hot-spot" formation) whereby due to emitter contact non-uniformity or non-uniform temperature profile, one emitter finger conducts progressively larger amounts of current. The formation of "hot-spots" is undesirable from a reliability standpoint.